The invention relates to a duct system with a throttle valve, especially an air intake duct of an internal combustion engine in which a throttle valve is arranged pivotably in a cross section of the duct. Furthermore, the invention relates to a throttle valve for installation in such a duct system. The invention also relates to a process for controlling a throttle valve in an air intake duct of an internal combustion engine.
It is generally known use throttle valves to close and to open the cross-section of an air intake duct for combustion air for an internal combustion engine. Furthermore, these throttle valves can also be utilized in a partially opened state. This use offers the advantage of reducing the air intake noise in operating ranges of the motor in which the complete cross-section of the air intake duct is not needed to provide combustion air. This occurs through partial closure of the throttle valve. In this way, the cross-sectional area of the flow channel on the raw air side is maintained as small as possible while matched to the operating condition. At the full power operating point, the supply of air to the motor is assured by complete opening of the cross-section of the duct. The remaining cross-sectional area between the wall of the duct and the throttle valve can be adjusted, for example, proportionally to the required mass flow. This achieves in a first approximation the same average rate of flow in the vicinity of the throttle valve.
The continuous adjustment of the throttle valve, however, raises problems. When small cross-sectional areas are required, narrow gaps result between the wall of the duct and the throttle valve which can lead to unfavorable flow conditions. Particularly, if the throttle valve and the cross-section of the duct have a round configuration, a whistling noise, which is more unpleasant than the intake 10 air noise that is to be avoided, can arise through the resulting sickle-shaped gap.
One possibility for solving this problem is proposed in European patent EP 889 228. According to this proposal the intake duct of the internal combustion engine has two partial cross sections which are separated from each other by an intermediate wall. The throttle valve is disposed in only one of the partial cross-sections, so that at low rotational speeds (rpm) of the motor, the one partial cross-sectional area of the intake duct can be closed. In this way a reduction of the air intake noise can be achieved.
The multi-chamber profile of the described air intake arrangement, however, causes additional expense. A higher expenditure for materials results, which also leads to an increase in the overall weight of the air intake system and makes the manufacturing process more difficult. For these reasons the proposed solution is less economical, and therefore its use is precluded at the least in modestly priced variants of motor vehicle lines.
It is the object of the invention therefore, to provide a device for decreasing the cross-section of a duct system which is reliable in operation and inexpensive to manufacture and which exhibits favorable acoustic characteristics.
These and other objects of the invention are achieved by the throttle apparatus and by the process for controlling a throttle valve which are described and claimed hereinafter.
The duct system of the invention includes a throttle valve which is pivotably arranged in a cross section of the duct system. The duct system conducts a fluid which is to be throttled. In accordance with the invention, however, the throttle valve is dimensioned such that in the closed position it leaves a residual cross-sectional area open. The term xe2x80x9cclosed positionxe2x80x9d refers to that position of the throttle valve in which it covers or closes off the maximum surface of the cross-sectional area which is to be throttled. If the throttle valve has a flat construction, then the closed position is achieved when the surface of the throttle valve is positioned perpendicular to the direction of flow of the fluid stream through the duct.
In contrast to conventional throttle valves, however, in this closed position the residual cross-section remains open and available for passage of fluid. If the throttle valve is utilized in the intake region of the air intake duct of an internal combustion engine, then a complete closure of the air intake cross section is not desired. Therefore, the throttle valve can be dimensioned such that in the closed position it does not completely cover the cross-section of the air intake duct. The perpendicular orientation of the valve is of great advantage from an acoustic point of view. In this way it is possible to for the throttle valve to reflect the sound waves which pass from the internal combustion engine through the air intake duct to the mouth of the air intake. This leads to a reduction in the air intake noise, since the sound waves cannot leave the system through the air intake opening. The reflected sound waves are superimposed over incoming ones, which may lead to a partial or complete cancellation or suppression.
In this way the air intake noise of the internal combustion engine can be decreased, primarily in the lower and medium rotational speed ranges. At the same time, whistling noises, like those which arise with conventional throttle valves when they are closed up to a tiny remaining gap, are prevented. In order to prevent the whistling noises, the residual cross section is advantageously designed to have an annular configuration around the throttle valve. It is not necessary thereby for the throttle valve to have a round configuration. An oval or a rectangular configuration is just as possible, wherein the cross-section of the duct system must match the form of the valve flap.
The throttle valve can be driven by various types of actuators. Candidates include, for example, electrical step motors or continuously adjustable vacuum boxes. A stepped adjustment of the throttle valve is also possible. Even an embodiment with only two steps, i.e. a closed throttle valve and an open throttle valve, which can be economically controlled with a vacuum box, will result in the acoustic advantages described above. However, then the acoustics of the intake duct cannot be continuously adapted to the operating conditions of the internal combustion engine. Instead, operating ranges must be defined in which the different step positions of the throttle valve are used.
In accordance with one particularly advantageous embodiment of the invention, the throttle valve is arranged in the narrowest cross-section of a duct section having a venturi-form cross-sectional configuration. The venturi-form configuration of the duct likewise has an advantageous effect on the acoustics of the intake duct.
It is not necessary for the throttle valve to be round. Instead it can take different forms, for example rectangular. The cross-section of the associated duct section must be appropriately matched to the form of the valve flap. Accordingly, the residual cross-sectional area surrounding the throttle valve and bounded by the walls of the duct system also does not have to be round. Instead, the annular residual cross-section is matched to the contours of the valve flap and the duct. The important thing in the configuration of the residual cross-sectional area is merely that regardless of the position of the valve flap, no regions are produced in which the spacing between the edge of the valve flap and the wall of the duct system is so small that whistling noises can arise.
The acoustic effects described above can be utilized especially efficiently if the residual cross-section amounts to a surface portion equal to from 10 to 40 percent of the overall surface area of the cross-section in which the throttle valve is positioned. In this way, on the one hand, a sufficiently large cross-section is available for operating conditions of the motor which require a maximum amount of air, and on the other hand, the cross-sectional area can be effectively decreased by the throttle valve.
A throttle valve, which when installed in the duct system described above leads to optimal results with regard to the acoustics of the duct system, has the advantages according to the invention. This means that the air flow noises of the fluid being conducted are minimized and sound waves in the interior of the duct system are suppressed.
In order to achieve favorable air intake acoustics throughout the entire rotational speed range of the internal combustion engine when the throttle valve is utilized in the air intake duct of an internal combustion engine, a control process is utilized in which the position of the valve flap is adjusted depending on the amount of combustion air required by the internal combustion engine. Various parameters can thereby be utilized as measured control values. A simple and economical solution results when the rotational speed n of the internal combustion engine is utilized as an adjusting parameter for the angle a of the valve flap. In most operating conditions of the motor, the rotational speed of the engine is proportional to its air requirements. At low rotational speeds, then, the throttle valve can be closed more and more until it reaches its closed position. In the upper rotational speed range the throttle valve is completely opened so that only the projection of the edge of the flap decreases the cross-sectional area of the air intake duct.
In every case, the process for controlling the throttle valve must assure that the internal combustion engine is provided with the minimally required amount of air in every operating state. It may, however, also be advantageous in certain operating states, not to limit the air to the necessary minimum, but instead to make a larger cross-sectional area available. This has the consequence that the air intake noise is greater than the minimum value which can be achieved. This is useful, for example, in the acceleration phase of the motor to give the driver an acoustical feedback from the internal combustion engine. In this way the driver can better recognize the appropriate time points for shifting gears. However, if the motor is operated at a constant rotational speed (rpm) for a longer period of time, then it is desirable to have the lowest possible air intake noise.
An appropriate control of the throttle valve can be achieved if the acceleration of the motor is additionally detected as a signal. In conjunction with this, a detection of the vacuum prevailing in the intake duct can be used as a supplemental control parameter by means of which an insufficient supply of combustion air to the internal combustion engine can be prevented in any event.
These and other features of preferred embodiments of the invention, in addition to being set forth in the claims, are also disclosed in the specification and/or the drawings, and the individual features each may be implemented in embodiments of the invention either individually or in the form of subcombinations of two or more features and can be applied to other fields of use and may constitute advantageous, separately protectable constructions for which protection is also claimed.